From DE 196 50 265 C1 a cross-arm window lifter is known whose drive arm is fixedly connected to a toothed segment in the geometrical center of which lies the pivotal axis which is disposed in a base plate. The drive arm is driven by a pinion which engages in the teeth of the toothed segment and which serves as the driven gear element of a motorized or manual drive. At a distance from the pivotal axis of the toothed segment is an articulated cross-arm joint through which the drive lever is connected for articulation to a second lever, the guide arm. One end of each lever arm is connected to sliders which are mounted substantially horizontally displaceable in guide areas of a first slideway fixed on the lower edge of the window. The other end of the guide arm is guided along a second guide rail which is fixed on the door body underneath the first guide rail. The guide arm is hereby controlled relative to the drive arm when the window lifter is actuated.
The window lifter construction described above has proved disadvantageous as far as its sensitivity to tolerance is concerned because the second guide rail fixed in the door body and dedicated to the guide arm has to be positioned relatively accurately with respect to the pivotal axis of the drive arm mounted on the base plate in order to ensure accurate lowering of the window pane. Furthermore the window lifter has a high material requirement and a correspondingly high weight.
A comparatively compact window winding arm is described in DE 198 28 891 C1. This window lifter also has a base plate on which a drive arm with a toothed segment is pivotally mounted, as well as a guide arm which is pivotally connected to the drive arm through an articulated joint. As opposed to the design previously described the second guide rail dedicated to the door body was replaced by a toothed arc with internal toothing in which external toothing connected to the guide lever engages. The external toothing thereby extends concentric with the articulated axis through which the two lever arms are connected together. During raising and lowering of the window pane the guide arm is controlled through the toothed arc, which extends concentric with the pivotal axis of the toothed segment, and the associated external toothing of the guide arm.
The drawback of this window lifter is its large number of parts, particularly with respect to the toothed elements required which furthermore places high demands on compensating the tolerances.
From DE 43 25 080 A1 an adjusting device is known for a window winding arm which is attached to the pane-side end of the one arm. When this adjusting device is actuated the connecting point of this lever arm is changed relative to the connecting point of the other lever arm so that the position of the external contour of the window pane is aligned sufficiently precisely relative to the contour of the window frame. The drawback of this device is that the adjustment can only be undertaken in a relatively widely lowered position of the window pane which makes adjustment difficult since the result of the adjustment can only be assessed after repeatedly closing the window and then corrected several times where necessary. Furthermore the entire adjustment path which may be necessary has to be allowed for in the adjusting device.
Another possibility for adjusting the cross arm window lifter is shown in DE 44 38 385 A1. For the purpose of adjustment the end opposite the window end of the guide lever is mounted adjustable in a separate rail fixed in the door. This adjusting device is very space-intensive.